Polymer ptc thermistor and temperature sensor

ABSTRACT

The present invention relates to a polymer PTC thermistor and a temperature sensor using the same. The polymer PTC thermistor, including a conductive polymer  1  having PTC characteristics and electrodes  2  and  3  joined to the conductive polymer  1,  characterized in that the electrodes  2  and  3  are provided along two sides  1   a  and  1   b  of the plate-like conductive polymer  1  and are separated from the edges of the sides  1   a  and  1   b,  and resin films  4  and  5  are formed which cover the sides  1   a  and 1 b  so as to wrap the electrodes  2  and  3.

TECHNICAL FIELD

The present invention relates to a polymer PTC thermistor and to a temperature sensor using the same.

BACKGROUND ART

A polymer PTC thermistor is a device which interrupts the passage of current by using a positive resistance temperature characteristic, that is, a PTC (Positive Temperature Coefficient) of a conductive polymer which is varied in conductivity due to thermal expansion.

Referring to FIG. 6, an example of the polymer PTC thermistor will be described below. FIG. 6 is a perspective view showing a conventional polymer PTC thermistor. In FIG. 6, reference numeral 101 denotes a conductive polymer, reference numerals 102 and 103 denote electrodes joined to the conductive polymer 101, and reference numerals 104 and 105 denote nonconductive resin films for covering the electrodes 102 and 103, which are provided between the conductive polymer and the resin films 104 and 105.

The conductive polymer 101 is rectangular in plan view and is shaped like a plate with a uniform thickness. For example, the conductive polymer 101 is a polymer resin body which is obtained by kneading polyethylene and carbon black and then forming crosslinkages by using radiation. In the conductive polymer 101, carbon black particles are linked to one another at room temperature and thus form a number of conductive paths through which current flows, thereby exhibiting excellent conductivity. However, when the conductive polymer 101 thermally expands due to a rise in ambient temperature around the conductive polymer 101 and excessive current passing through the conductive paths, a distance between the carbon black particles is increased so as to cut off the conductive paths, thereby sharply reducing conductivity (resistance increases).

The electrodes 102 and 103 are provided respectively on both ends of the longitudinal direction of the plate-like conductive polymer 101. The electrode 102 is constituted of a copper electrode strip 102 a provided along a side 101 a of the conductive polymer 101, a base 102 b which is connected to the electrode strip 102 a and is provided on one end of the conductive polymer 101, and a nickel foil 102 c disposed between the conductive polymer 101 and the electrode strip 102 a.

The electrode 103 is similar in structure to the electrode 102. The electrode 103 is constituted of a copper electrode strip 103 a provided along the other side 101 b of the conductive polymer 101, a base 103 b which is connected to the electrode strip 103 a and is provided on the other end of the conductive polymer 101, and nickel foil 103 c disposed between the conductive polymer 101 and the electrode strip 103 a.

The electrode strip 102 a has the same width as the conductive polymer 101 and has one end formed into a rectangle. The electrode strip 102 a is formed with a gap which is in parallel with the electrode 103 (electrode strip 103 d described later) on the opposite side. The base 102 b is formed by integrating the electrode strip 102 a and a copper electrode strip 102 d, which partially remains on the other side 101 b, with a solder coating layer 102 e.

The electrode strip 103 a has the same width as the conductive polymer 101 and has one end formed into a rectangle. The electrode strip 103 a is formed with a gap which is in parallel with the electrode 102 (the above electrode strip 102 d) on the opposite side. The base 103 b is formed by integrating the electrode strip 103 a and a copper electrode strip 103 d, which partially remains on the side 101 a, with a solder coating layer 103 e.

The resin film 104 is formed so as to cover the electrode strip 102 a except for the base 102 b and the electrode strip 102 d on the side 101 a of the conductive polymer 101. The resin film 105 is also formed so as to cover the electrode strip 103 a except for the base 103 b and the electrode strip 103 d on the side 101 b of the conductive polymer 101.

By using the PTC characteristic of the conductive polymer 101, the polymer PTC thermistor thus configured can be caused to act as a switch using the ambient temperature of the conductive polymer 101 as a trigger. When the ambient temperature is lower than a predetermined temperature (temperature at which the conductive polymer thermally expands), current is applied. When the ambient temperature is equal to or higher than the predetermined temperature, the conductive polymer 101 thermally expands and interrupts the current.

The polymer PTC thermistor can be caused to act as a switch using as a trigger the magnitude of current flowing between the electrodes 102 and 103. When overcurrent occurs between the electrodes 102 and 103, the conductive polymer 101 thermally expands and interrupts current due to self-heating caused by Joule heat. When excessive current is eliminated, the PTC thermistor returns to a state enabling the passage of current.

In the polymer PTC thermistor, the electrode strip 102 a is overlaid on one side of the conductive polymer 101 and thus the side edges of the electrode strip 102 a and the nickel foil 102 c are exposed from the side edges of the longitudinal direction of the conductive polymer 101. Similarly the electrode strip 103 a is overlaid on the other side of the conductive polymer 101 and thus the side edges of the electrode strip 103 a and the nickel foil 103 c are exposed from the side edges of the longitudinal direction of the conductive polymer 101.

Incidentally the side edges of the electrode strips 102 a and 103 a and the nickel foils 102 c and 103 c are exposed to the air all the time and thus are susceptible to moisture in the air. Thus, oxidation gradually occurs over time. Such oxidation considerably develops particularly between the conductive polymer 101 and the nickel foils 102 c and 103 c and becomes a factor causing a poor contact and interrupting the passage of current, thereby affecting the performance of the polymer PTC thermistor. Hence, oxidation is a serious problem. In addition, the need for miniaturization of polymer PTC thermistors has increased in recent years (e.g., the size of the conductive polymer 101 is long side×short side×thickness; 1.60 mm×0.80 mm×0.62 mm or less). The smaller the polymer PTC thermistor, the more the contact surface between a conductive polymer and an electrode strip decreases. Hence, even slight oxidation is likely to cause poor contact.

Further, the side edges of the electrode strips 102 a and 103 a are exposed in the above polymer PTC thermistor. Thus, for example when the polymer PTC thermistor is soldered onto a circuit board of electrical equipment, a residue of solder may adhere over the electrode strips 102 a and 103 a, cause a short circuit, and interfere with the switching function. Hence, such a configuration causes a problem.

DISCLOSURE OF THE INVENTION

In order to solve the above problems, the following means are adopted.

The present invention relates to a polymer PTC thermistor comprising a conductive polymer having a PTC characteristic and an electrode joined to the conductive polymer, characterized in that the electrode is disposed along a side having the conductive polymer and is separated from the edge of the side, and a resin film covers the side so as to wrap the electrode.

In the present invention, the electrode is disposed along the side having the conductive polymer and is separated from the edge of the side and the resin film is formed which covers the side so as to wrap the electrode, so that the electrode is separated from a boundary of the conductive polymer and the resin film, the boundary being susceptible to oxidation first, and the electrode is covered with the resin film on the conductive polymer. Thus, water does not enter between the conductive polymer and the electrode and oxidation is prevented on the electrode. Further, a corrosion-resistant region is formed in which the conductive polymer and the resin film are overlaid to prevent the entry of water around the electrode. This configuration also prevents oxidation on the electrode.

In the present invention, it is desirable to form a conductive polymer into a plate, dispose electrodes respectively on the two sides of the conductive polymer, and form resin films which respectively cover the two sides so as to wrap the electrodes. With this configuration, the electrodes can be readily attached to the conductive polymer and the resin films covering the electrodes can be readily formed, thereby improving productivity in the manufacturing of the polymer PTC thermistor.

Further, in the present invention, two electrodes may be separately provided on one side of the conductive polymer and a resin film may be formed which covers the side so as to wrap the two electrodes. Also with this configuration, the electrodes can be readily attached to the conductive polymer and the resin film covering the electrodes can be readily formed, thereby improving productivity in the manufacturing of the polymer PTC thermistor.

The polymer PTC thermistor having the above characteristics can be used as a temperature sensor element because of a switching function using an ambient temperature as a trigger. The polymer PTC thermistor is particularly suitable for a temperature sensor.

The thermal expansion temperature, that is, a temperature at which the conductive paths are interrupted, can be arbitrarily set by changing the composition of the conductive polymer or adjusting the amount of carbon black. Thus, by setting the thermal expansion temperature of the conductive polymer at a certain value, it is decided that the temperature of an object is lower than the certain value when current passes through the two electrodes and it is decided that the temperature exceeds the certain value when the current is interrupted. In this way, by using the polymer PTC thermistor of the present invention as a temperature sensor element, it is possible to clearly measure a temperature while narrowing a target temperature range.

For example, the polymer PTC thermistor is mounted on the circuit board of each kind of electrical equipment, the polymer PTC thermistor of the present invention having the conductive polymer whose thermal expansion temperature is set in consideration of an upper limit temperature permitting normal operations of the circuit board. Thus, the circuit is interrupted in the event of abnormal heat on the board, thereby protecting the electrical equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a polymer PTC thermistor according to Embodiment 1 of the present invention, FIG. 1A is a plan view showing the polymer PTC thermistor, FIG. 1B is a back view, FIG. 1C is a front view, FIG. 1D is a rear view, FIG. 1E is a left side view, and FIG. 1F is a right side view;

FIG. 2 is a perspective view showing the polymer PTC thermistor of Embodiment 1;

FIG. 3 is a diagram showing the manufacturing process of the polymer PTC thermistor of Embodiment 1 in stages;

FIG. 4 is a diagram showing a polymer PTC thermistor according to Embodiment 2 of the present invention of the present invention, FIG. 4A is a plan view showing the polymer PTC thermistor, FIG. 4B is a back view, FIG. 4C is a front view, FIG. 4D is a rear view, FIG. 4E is a left side view, and FIG. 4F is a right side view;

FIG. 5 is a diagram showing a polymer PTC thermistor according to Embodiment 3 of the present invention, FIG. 5A is a plan view showing the polymer PTC thermistor, FIG. 5B is a back view, FIG. 5C is a front view, FIG. 5D is a rear view, FIG. 5E is a left side view, and FIG. 5F is a right side view; and

FIG. 6 is a perspective view showing a conventional polymer PTC thermistor.

BEST MODE FOR CARRYING OUT THE INVENTION EMBODIMENT 1

Referring to FIGS. 1 to 3, Embodiment 1 of the present invention will be described below. FIG. 1A is a plan view showing a polymer PTC thermistor according to the present embodiment. FIG. 1B is a back view, FIG. 1C is a front view, FIG. 1D is a rear view, FIG. 1E is a left side view, and FIG. 1F is a right side view. FIG. 2 is a perspective view showing the polymer PTC thermistor according to the present embodiment.

The polymer PTC thermistor is used, for various kinds of electrical equipment, as a temperature sensor element aimed at protecting an overheated circuit board. In the drawings, reference numeral 1 denotes a conductive polymer, reference numerals 2 and 3 denote electrodes joined to the conductive polymer 1, and reference numerals 4 and 5 denote nonconductive resin films for covering the electrodes 2 and 3, which are provided between the conductive polymer and the resin films 4 and 5.

The conductive polymer 1 is rectangular in plan view and is shaped like a plate (long side×short side×thickness; 1.60 mm×0.80 mm×0.62 mm) with an even thickness. For example, the conductive polymer 1 is a polymer resin body which is obtained by kneading polyethylene and carbon black and then forming a cross-link by using radiation. In the conductive polymer 1, carbon black particles are linked to one another at room temperature and thus form a number of conductive paths through which current flows, thereby exhibiting excellent conductivity. However, when the conductive polymer 1 thermally expands due to a rise in the ambient temperature around the conductive polymer 1 and excessive current passing through the conductive paths, a distance between the carbon black particles is increased so as to cut off the conductive paths, thereby sharply reducing conductivity (resistance increases).

The electrodes 2 and 3 are provided respectively on both ends of the longitudinal direction of the conductive polymer 1. The electrode 2 is constituted of a copper electrode strip 2 a provided along a side 1 a of the conductive polymer 1, a base 2 b which is connected to the electrode strip 2 a and is provided on one end of the conductive polymer 1, and a nickel foil 2 c disposed between the conductive polymer 1 and the electrode strip 2 a.

The electrode 3 is similar in structure to the electrode 2. The electrode 3 is constituted of a copper electrode strip 3 a provided along the other side 1 b of the conductive polymer 1, a base 3 b which is connected to the electrode strip 3 a and is provided on the other end of the conductive polymer 1, and nickel foil 3 c disposed between the conductive polymer 1 and the electrode strip 3 a.

The electrode strip 2 a is shaped like a rectangle (length×width; 0.73 mm×0.40 mm) with a thickness of 20 to 30 μm except for the base. The electrode strip 2 a has the long side along the length of the conductive polymer 1 but is smaller in width than the conductive polymer 1. Two side edges 2 d along the longitudinal direction of the electrode strip 2 a are disposed at a distance of about 0.20 mm from the side edges of the conductive polymer 1. Further, the end of the electrode strip 2 a is formed into a rectangle disposed at a distance of about 0.27 mm from the electrode 3 (electrode strip 3 e described later) on the opposite side.

The base 2 b is formed by integrating the base end of the electrode strip 2 a and a copper electrode strip 2 e, which partially remains on the other side 1 b of the conductive polymer 1, along a concave portion 1 c formed on one end of the conductive polymer 1. A solder coating layer 2 f is formed on a surface of the base 2 b. The coating layer 2 f is about 20 to 35 μm in thickness.

The electrode strip 3 a is also formed like a rectangle having the same shape and dimensions as the electrode strip 2 a. The electrode strip 3 a has the long side along the length of the conductive polymer 1 but is smaller in width than the conductive polymer 1. Two side edges 3 d along the longitudinal direction of the electrode strip 3 a are disposed at a distance of about 0.20 mm from the side edges of the conductive polymer 1. Further, the end of the electrode strip 3 a is formed into a rectangle disposed at a distance of about 0.27 mm from the electrode 2 (the electrode strip 2 e) on the opposite side.

The base 3 b is formed by integrating the base end of the electrode strip 3 a and a copper electrode strip 3 e, which partially remains on the side 1 a of the conductive polymer 1, along a concave portion 1 d formed on the other end of the conductive polymer 1. A solder coating layer 3 f is formed on a surface of the base 3 b. The coating layer 3 f is about 20 to 35 μm in thickness.

The resin film 4 is formed so as to entirely cover the electrode strip 2 a except for the base 2 b and the electrode strip 2 e on the side 1 a of the conductive polymer 1 and the resin film 4 is about 10 to 15 μm in thickness. The resin film 5 is also formed so as to entirely cover the electrode strip 3 a except for the base 3 b and the electrode strip 3 e on the other side 1 b of the conductive polymer 1 and the resin film 5 is about 10 to 15 μm in thickness.

The polymer PTC thermistor thus configured uses the PTC characteristic of the conductive polymer 1 and acts as a switch using ambient temperature as the trigger. The thermal expansion temperature, that is, a temperature interrupting the conductive paths, can be arbitrarily set by changing the composition of the conductive polymer 1 or adjusting the amount of carbon black. Thus, when it is necessary to know whether or not the temperature of an object exceeds a certain value, the composition of the conductive polymer 1 is changed or the amount of carbon black is adjusted to set the thermal expansion temperature of the conductive polymer 1 at the certain value. When current is applied between the electrodes 2 and 3, it is decided that the temperature of the object is lower than the certain value. When the current is interrupted, it is decided that the temperature exceeds the certain value. In this way, the polymer PTC thermistor is used as a temperature sensor element.

Additionally for example, a polymer PTC thermistor is mounted on the circuit board of each kind of electrical equipment, the polymer PTC thermistor having the conductive polymer 1 whose thermal expansion temperature is set in consideration of an upper limit temperature permitting normal operations of the circuit board. Thus, the circuit is interrupted in the event of abnormal heat on the board, thereby protecting the electrical equipment.

In either case, the way to activate the thermistor is similar to that of a conventional polymer PTC thermistor, and thus the explanation thereof is omitted.

Referring to FIG. 3, the manufacturing steps of the polymer PTC thermistor will be described below. FIGS. 3A to 3E are sectional views showing the states of the polymer PTC thermistor in the manufacturing steps.

First, as shown in FIG. 3A, a work 13 is prepared in which nickel foils 12 are attached by pressure to both sides of a raw plate 11 of a conductive polymer having an even thickness. This part acts as the conductive polymer 1 of the polymer PTC thermistor at some other time.

A plurality of lines of through holes 14 with equal pitches are formed at regular intervals on the work 13. The respective parts of the polymer PTC thermistor are formed between the adjacent lines of the through holes 14. Final products are made by cutting the work 13. Besides, the through holes 14 in the adjacent lines act as the concave portions 1 c and 1 d.

As shown in FIG. 3B, a copper plating layer 15 is formed over both sides of the work 13 and the inner surfaces of the through holes 14. This part acts as the electrodes 2 and 3.

As shown in FIG. 3C, etching is performed on predetermined portions on both sides of the work 13 to remove the copper plating layer 15 and the nickel foil 12, and the surface of the raw plate 11 of the conductive polymer is exposed from the etched portions. These portions act as gaps between the electrode strips 2 a and 3 e.

As shown in FIG. 3D, a resin layer 16 is formed so as to cover a predetermined portion on the copper plating layer 15 and the portion where the raw plate 11 of the conductive polymer is exposed. This portion acts as the resin films 4 and 5.

As shown in FIG. 3E, the resin layer 16 is used instead of a mask and a solder plating layer 17 is formed on the other portions (including the inner surfaces of the hole 14). This portion acts as the solder coating layers 2 f and 3 f. Thereafter the work 13 is cut along the lines of the through holes 14 and is further cut in parallel with the paper face of FIG. 3, so that the polymer PTC thermistors are obtained as final products.

In the polymer PTC thermistor thus configured, for example, the side edge 2 d of the electrode strip 2 a is separated from the side edge of the conductive polymer 1 while the electrode strip 2 a is formed along the side 1 a of the conductive polymer 1, and the side 1 a is covered with the resin film 4 together with the electrode strip 2 a, so that the electrode strip 2 a is separated from the boundary of the conductive polymer 1 and resin film 4, the boundary being susceptible to oxidation first, and the electrode strip 2 a is entirely covered with the resin film 4 and is not exposed to the air. Thus, it is possible to prevent oxidation on the electrode strip 2 a. Further, a corrosion-resistant region is formed in which the conductive polymer 1 and the resin film 4 are overlaid to prevent the entry of water around the electrode strip 2 a. This configuration also prevents oxidation on the electrode strip 2 a. This effect can be similarly anticipated on the electrode strip 3 a.

Moreover, in the polymer PTC thermistor thus manufactured, the two electrode strips 2 a and 3 a are respectively disposed on both sides of the conductive polymer 1 shaped like a plate. Thus, the electrodes 2 and 3 can be readily attached to the conductive polymer 1 and the resin films 4 and 5 covering the electrode strips 2 a and 3 a can be readily formed, thereby improving productivity.

Additionally, the resin films 4 and 5 are formed so as to entirely cover the electrode strips 2 a and 3 a in the present embodiment. Considering the prevention of oxidation developing between the conductive polymer 1 and the electrode strips 2 a and 3 a, the following configuration is also applicable: the resin films cover at least a region which includes the boundary of the conductive polymer 1 and the electrode strip 2 a and is exposed to the outside and a region which includes the boundary of the conductive polymer 1 and the electrode strip 3 a and is exposed to the outside.

EMBODIMENT 2

Referring to FIG. 4, Embodiment 2 of the present invention will be described below. FIG. 4A is a plan view showing a polymer PTC thermistor according to the present embodiment. FIG. 4B is a back view, FIG. 4C is a front view, FIG. 4D is a rear view, FIG. 4E is a left side view, and FIG. 4F is a right side view. The constituent elements described in Embodiment 1 are indicated by the same reference numerals and the explanation thereof is omitted.

The present embodiment is different from Embodiment 1 in the configurations of electrodes 12 and 13. The electrode 12 is constituted of a copper electrode strip 12 a provided along a side 1 a of a conductive polymer 1, a copper electrode strip 12 b provided along the other side 1 b, a base 12 c provided over the electrode strips 12 a and 12 b on one end of the conductive polymer 1, and nickel foils 12 d respectively disposed between the conductive polymer 1 and the electrode strips 12 a and 12 b.

The electrode 13 is similar in structure to the electrode 12. The electrode 13 is constituted of a copper electrode strip 13 a provided along a side 1 a of the conductive polymer 1, a copper electrode strip 13 b provided along the other side 1 b, a base 13 c provided over the electrode strips 13 a and 13 b on the other end of the conductive polymer 1, and nickel foils 13 d disposed respectively between the conductive polymer 1 and the electrode strips 13 a and 13 b.

The electrode strip 12 a is shaped like a tongue which is a right triangle having a diagonally cut end (length; 0.73 mm). A side edge 12 e is caused to agree with the longitudinal direction of the conductive polymer 1 and is disposed at a distance of about 0.10 mm from the side edge of the conductive polymer 1.

The electrode strip 13 a is also shaped like a tongue which is a right triangle having a diagonally cut end with the same shape and dimensions as the electrode strip 12 a. A side edge 13 e adjacent to a hypotenuse is caused to agree with the longitudinal direction of the conductive polymer 1 and is disposed at a distance of about 0.10 mm from the side edge of the conductive polymer 1. The electrode strips 12 a and 13 a are disposed at a distance of about 0.27 mm from each other with the hypotenuses facing each other in parallel on the side 1 a of the conductive polymer 1. The distance is to be set larger than the thickness of the conductive polymer 11.

The electrode strips 12 b and 13 b are arranged on the other side 1 b of the conductive polymer 1 in the same manner as the electrode strips 12 a and 13 a. The side edges 12 e and 13 e adjacent to hypotenuses are caused to agree with the longitudinal direction of the conductive polymer 1 and are disposed at a distance of about 0.10 mm from the side edges of the conductive polymer 1. Further, the hypotenuses on the ends are faced to each other in parallel and are disposed at a distance of about 0.27 mm from each other.

The base 12 c is formed by integrating the electrode strips 12 a and 12 b along a concave portion 1 c. A solder coating layer 12 f is formed on a surface of the base 12 c. The base 13 c is formed by integrating the electrode strips 13 a and 13 b along a concave portion 1 d in the same manner as the base 12 c. A solder coating layer 13 f is formed on a surface of the base 13 c. The coating layers 12 f and 13 f are about 20 to 35 μm in thickness.

The resin film 4 is formed so as to entirely cover the electrode strips 12 a and 13 a except for the bases 12 c and 13 c on the side 1 a of the conductive polymer 1. The resin film 5 is formed so as to entirely cover the electrode strips 12 b and 13 b except for the bases 12 c and 13 c on the other side 1 b of the conductive polymer 1.

As with Embodiment 1, the polymer PTC thermistor configured thus has a switching function using ambient temperature as the trigger and a switching function using as the trigger the magnitude of current flowing between the electrodes 12 and 13. The thermistor is activated in a similar manner and thus the explanation thereof is omitted. Further, the manufacturing steps of the polymer PTC thermistor are similar to those of Embodiment 1 and thus the explanation thereof is also omitted.

In the polymer PTC thermistor thus configured, for example, the side edge 12 e of the electrode strip 12 a is separated from the side edge of the conductive polymer 11 while the electrode strip 12 a is formed along the side 1 a of the conductive polymer 11, and the side 1 a is covered with the resin film 4 together with the electrode strip 12 a, so that the electrode strip 12 a is separated from the boundary of the conductive polymer 1 and resin film 4, the boundary being susceptible to oxidation first, and the electrode strip 12 a is entirely covered with the resin film 4 and is not exposed to the air. Thus, it is possible to prevent oxidation on the electrode strip 12 a. Further, a corrosion-resistant region is formed in which the conductive polymer 1 and the resin film 4 are overlaid to prevent the entry of water around the electrode strip 12 a. This configuration also prevents oxidation on the electrode strip 12 a. This effect can be similarly expected on the electrode strips 12 b, 13 a, and 13 b.

EMBODIMENT 3

Referring to FIG. 5, Embodiment 3 of the present invention will be described below. FIG. 5A is a plan view showing a polymer PTC thermistor according to the present embodiment. FIG. 5B is a back view, FIG. 5C is a front view, FIG. 5D is a rear view, FIG. 5E is a left side view, and FIG. 5F is a right side view. The constituent elements described in the above embodiments are indicated by the same reference numerals and the explanation thereof is omitted.

The present embodiment is different from the above embodiments in the configurations of electrodes 22 and 23. The electrode 22 is constituted of a copper electrode strip 22 a provided along a side 1 a of a conductive polymer 1, a base 22 b which is connected to the electrode strip 22 a and is provided on one end of the conductive polymer 1, and a nickel foil 22 c disposed between the conductive polymer 1 and the electrode strip 22 a.

The electrode 23 is similar in structure to the electrode 22. The electrode 23 is constituted of a copper electrode strip 23 a provided along the side 1 a of the conductive polymer 1, a base 23 b which is connected to the electrode strip 23 a and is provided on the other end of the conductive polymer 1, and a nickel foil 23 c disposed between the conductive polymer 1 and the electrode strip 23 a. Constituent elements corresponding to the electrode strips 22 a and 23 a are not provided on the other side 1 b of the conductive polymer 1.

The electrode strip 22 a is shaped like a plow whose teeth 22 d are about 0.90 mm in length and about 0.10 mm in width. An interval between the adjacent teeth is about 0.30 mm. The longitudinal direction of the tooth 22 d is caused to agree with that of the conductive polymer 1. The electrode strip 23 a is also shaped like a plow with the same shape and dimensions as the electrode strip 22 a. The longitudinal direction of a tooth 23 d is caused to agree with that of the conductive polymer 1. The teeth of the electrode strips 22 a and 23 a are alternately combined so as to face each other. The alternately combined teeth 22 d and 23 d are disposed at a distance of about 0.10 mm. The teeth 22 d and 23 d arranged on the outer side of the width direction of the conductive polymer 1 are respectively disposed at a distance of about 0.05 mm from the side edges of the conductive polymer 1.

The base 22 b is formed by integrating the base end of the electrode strip 22 a and a copper electrode strip 22 e, which partially remains on the other side 1 b of the conductive polymer 1, along a concave portion 1 c. A solder coating layer 22 f is formed on a surface of the base 22 b. The base 23 b is also formed by integrating the base end of the electrode strip 23 a and a copper electrode strip 23 e, which partially remains on the other side 1 b, along the concave portion 1 c in the same manner as the base 22 b. A solder coating layer 23 f is formed on a surface of the base 23 b. The coating layers 22 f and 23 f are about 20 to 35 μm in thickness.

The resin film 4 is formed so as to entirely cover the electrode strips 22 a and 23 a except for the bases 22 b and 23 b on the side 1 a of the conductive polymer 1. The resin film is formed so as to entirely cover the other side 1 b of the conductive polymer 1 except for the electrode strips 22 e and 23 e.

As with above embodiments, the polymer PTC thermistor configured thus has a switching function using ambient temperature as the trigger and a switching function using as a trigger the magnitude of current flowing between the electrodes 22 and 23. The thermistor is activated in a similar manner and thus the explanation thereof is omitted. Further, the manufacturing steps of the polymer PTC thermistor are similar to those of Embodiment 1 and thus the explanation thereof is also omitted.

In the polymer PTC thermistor thus configured, the electrode strips 22 a and 23 a shaped like plows are arranged so that the teeth 22 d and 23 d are alternately combined and are separated from the side edges of the conductive polymer 1. Further, the side 1 a is covered with the resin film 4 together with the electrode strips 22 a and 23 a, so that the electrode strips 22 a and 23 a are separated from the boundary of the conductive polymer 1 and resin film 4, the boundary being susceptible to oxidation first, and the electrode strips 22 a and 23 a are entirely covered with the resin film 4 and are not exposed to the air. Thus, it is possible to prevent oxidation on the electrode strips 22 a and 23 a. Further, a corrosion-resistant region is formed in which the conductive polymer 1 and the resin film 4 are overlaid to prevent the entry of water around the electrode strips 22 a and 23 a which are combined with each other. This configuration also prevents oxidation on the electrode strips 22 a and 23 a.

Moreover, in the polymer PTC thermistor thus manufactured, the electrodes 22 and 23 can be readily attached to the conductive polymer 1 and the resin film 4 covering the electrode strips 22 a and 23 a can be readily formed, thereby improving productivity in the manufacturing of the polymer PTC thermistor.

Each of the embodiments described the example using the polymer PTC thermistor as a temperature sensor element aimed at protecting an overheated circuit board. The polymer PTC thermistor of the present invention can also be caused to act as a switch using as the trigger the magnitude of current flowing between the electrodes 2 and 3. In this application, the polymer PTC thermistor is used as an overcurrent protection device aimed at preventing overcharging in a secondary battery such as a lithium-ion secondary battery, a nickel metal hydride secondary battery, and a nicad secondary battery.

Industrial Applicability

According to the polymer PTC thermistor of the present invention, an electrode is disposed along one side of a conductive polymer so as to be separated from the edge of the side, and a resin film is formed which covers the side so as to wrap the electrode, so that the electrode is separated from the boundary of the conductive polymer and resin film, the boundary being susceptible to oxidation first, and the electrode strip is covered with the resin film on the conductive polymer. Water does not enter between the conductive polymer and the electrode and oxidation is prevented on the electrode, thereby preventing the polymer PTC thermistor from decreasing in performance, which is degraded by oxidation. Further, a corrosion-resistant region is formed in which the conductive polymer and the resin film are overlaid to prevent the entry of water around the electrode. This configuration also prevents oxidation on the electrode and prevents the polymer PTC thermistor from decreasing in performance.

According to the polymer PTC thermistor of the present invention, the conductive polymer is formed into a plate, electrodes are provided respectively on the two sides of the conductive polymer, and a resin film is formed which covers the two sides so as to wrap the electrodes, so that the electrodes can be readily attached to the conductive polymer and the resin layer covering the electrodes can be readily formed, thereby improving productivity in the manufacturing of the polymer PTC thermistor.

According to the polymer PTC thermistor of the present invention, two electrodes are separately provided on one side of the conductive polymer and a resin film is formed which covers the side so as to wrap the two electrodes, so that the electrodes can be readily attached to the conductive polymer and the resin film covering the electrodes can be readily formed, thereby improving productivity in the manufacturing of the polymer PTC thermistor.

Moreover, according to the polymer PTC thermistor of the present invention, a temperature can be clearly detected by using the polymer PTC thermistor of the present invention as a temperature sensor element. For example, the polymer PTC thermistor is mounted on the circuit board of each kind of electrical equipment, the polymer PTC thermistor having the conductive polymer whose thermal expansion temperature is set in consideration of an upper limit temperature permitting normal operations of the circuit board. Thus, the circuit is interrupted in the event of abnormal heat on the board, thereby protecting the electrical equipment. 

1. A polymer PTC thermistor comprising: a conductive polymer having PTC characteristics, and an electrode joined to the conductive polymer, wherein the electrode is disposed along a side having the conductive polymer and is separated from an edge of the side, and a resin film covers the side so as to wrap the electrode.
 2. The polymer PTC thermistor according to claim 1, characterized in that a conductive polymer is formed in a plate, electrodes are provided respectively on two sides of the conductive polymer, and resin films respectively cover the two sides so as to wrap the electrodes.
 3. The polymer PTC thermistor according to claim 1, characterized in that two electrodes are separately provided on one side of the conductive polymer and the resin film covers the side so as to wrap the two electrodes.
 4. A temperature sensor characterized by using the polymer PTC thermistor according to claim 1 as a temperature sensor element.
 5. A temperature sensor characterized by using the polymer PTC thermistor according to claim 2 as a temperature sensor element.
 6. A temperature sensor characterized by using the polymer PTC thermistor according to claim 3 as a temperature sensor element. 